HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Services Conf - Page 11

Dynamic ARP entry, Static ARP entry, Configuring a static ARP entry

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Dynamic ARP entry ARP automatically creates and updates dynamic entries. A dynamic ARP entry is removed when its aging timer expires or the output interface goes down, and it can be overwritten by a static ARP entry. Static ARP entry A static ARP entry is manually configured and maintained. It does not age out, and cannot be overwritten by a dynamic ARP entry. Static ARP entries protect communication between devices, because attack packets cannot modify the IP-to-MAC mapping in a static ARP entry. Static ARP entries can be classified into long and short ARP entries. • To configure a long static ARP entry, specify the IP address, MAC address, VLAN, and output interface. A long static ARP entry is directly used for forwarding matching packets. To allow communication with a host using a fixed IP-to-MAC mapping through a specific interface in a specific VLAN, configure a long static ARP entry for it. • To configure a short static ARP entry, you only need to specify the IP address and MAC address. The device first sends an ARP request whose target IP address is the IP address of the short entry. If the sender IP and MAC addresses in the received ARP reply match the IP and MAC addresses of the short static ARP entry, the device adds the interface receiving the ARP reply to the short static ARP entry, and then the entry can be used for forwarding the matching IP packets. Configuring a static ARP entry A static ARP entry is effective when the device it corresponds to works properly. However, when a VLAN or VLAN interface is deleted, any static ARP entry corresponding to it will also be deleted (if it is a long static ARP entry) or will become unresolved (if it is a short and resolved static ARP entry). Follow these guidelines when you configure a long static ARP entry: • The vlan-id argument must be the ID of an existing VLAN where the ARP entry resides. The specified Ethernet interface must belong to that VLAN. The VLAN interface of the VLAN must be created. • The IP address of the VLAN interface of the VLAN specified by the vlan-id argument must belong to the same subnet as the IP address specified by the ip-address argument. To configure a static ARP entry: Step 1. Enter system view. 2. Configure a static ARP entry. Command Remarks system-view • Configure a long static ARP entry: arp static ip-address mac-address vlan-id interface-type interface-number [ vpn-instance vpn-instance-name ] • Configure a short static ARP entry: arp static ip-address mac-address [ vpn-instance vpn-instance-name ] N/A Use either command. 3

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3
Dynamic ARP entry
ARP automatically creates and updates dynamic entries. A dynamic ARP entry is removed when its aging
timer expires or the output interface goes down, and it can be overwritten by a static ARP entry.
Static ARP entry
A static ARP entry is manually configured and maintained. It does not age out, and cannot be overwritten
by a dynamic ARP entry.
Static ARP entries protect communication between devices, because attack packets cannot modify the
IP-to-MAC mapping in a static ARP entry.
Static ARP entries can be classified into long and short ARP entries.
•
To configure a long static ARP entry, specify the IP address, MAC address, VLAN, and output
interface. A long static ARP entry is directly used for forwarding matching packets. To allow
communication with a host using a fixed IP-to-MAC mapping through a specific interface in a
specific VLAN, configure a long static ARP entry for it.
•
To configure a short static ARP entry, you only need to specify the IP address and MAC address.
The device first sends an ARP request whose target IP address is the IP address of the short entry.
If the sender IP and MAC addresses in the received ARP reply match the IP and MAC addresses of
the short static ARP entry, the device adds the interface receiving the ARP reply to the short static
ARP entry, and then the entry can be used for forwarding the matching IP packets.
Configuring a static ARP entry
A static ARP entry is effective when the device it corresponds to works properly. However, when a VLAN
or VLAN interface is deleted, any static ARP entry corresponding to it will also be deleted (if it is a long
static ARP entry) or will become unresolved (if it is a short and resolved static ARP entry).
Follow these guidelines when you configure a long static ARP entry:
•
The
vlan-id
argument must be the ID of an existing VLAN where the ARP entry resides. The specified
Ethernet interface must belong to that VLAN. The VLAN interface of the VLAN must be created.
•
The IP address of the VLAN interface of the VLAN specified by the
vlan-id
argument must belong to
the same subnet as the IP address specified by the
ip-address
argument.
To configure a static ARP entry:
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Configure a static ARP
entry.
•
Configure a long static ARP entry:
arp static
ip-address mac-address vlan-id
interface-type interface-number
[
vpn-instance
vpn-instance-name
]
•
Configure a short static ARP entry:
arp static
ip-address mac-address
[
vpn-instance
vpn-instance-name
]
Use either command.